Table 2.
List of RFID tag antenna sensors for crack detection and characterization.
| Measurand | Sensing Principle (Antenna Type) | Sensing Variable | Feature | Pros. | Cons. | Refs. |
|---|---|---|---|---|---|---|
| Crack depth | Inductive (coil) | Potential drop | Voltage ratio | Resolution: 0.5 mm in depth | Location dependent; VNA is required | [108] |
| Crack (length) growth and orientation detection | 2D grid (meander line dipole) | Reflectometry | Time difference of arrival | Chipless; Large dynamic range | VNA is required | [32] |
| Crack (length) growth and orientation detection | Mode orthogonality (dual-resonant patch) | S11 | RFS | Resolution: sub-mm; Large dynamic range | VNA is required; not compatible with Gen2 regulation | [33] |
| Crack (length) growth and orientation detection | Spatial division (dual-resonant patch) | Backscattered power | Power variation | Multi-site crack | Dedicated receiver | [34] |
| Crack (length) growth and orientation detection | 2D Grid (dipole) | Backscattered power | Power variation | Read range: 1 m | Power is susceptible to wireless channel | [35] |
| Fatigue crack | Deformation (patch) | Turn on power | RFS | Read range: 2.1 m | Large antenna size | [36] |
| Crack (width) growth | Mutual coupling (patch antenna array) | Backscattered phase | Phase shift | Sub-mm resolution; Platform tolerance | Crack position should be known prior; | [37,100] |